1. Field of the Invention
The present invention relates to a laser irradiation apparatus and a method of laser irradiation in order to efficiently perform laser irradiation in a laser direct imaging method or the like. In addition, the present invention relates to a method for manufacturing a semiconductor device with the use of a process of the laser irradiation.
2. Description of the Related Art
In manufacturing processes of a semiconductor device, a printed board, and the like, with an integration of a circuit, microfabrication is essential. In general, such microfabrication is performed by a laser light-exposure technology in which a photo mask with a circuit pattern written therein is made preliminarily and the pattern is transferred to a substrate. However, the method which uses the photo mask spends cost and time for making the mask. Therefore, in recent years, a process without the photo mask (herein after referred to as maskless process) has drawn attention. As a typical maskless process, there is a laser direct imaging method. In the laser direct imaging method, a photosensitive material is discharged or applied on a conductive film formed by sputtering or the like. And upon the photosensitive material, a laser direct imaging apparatus is used to perform irradiation with a laser beam. At that time, the irradiation with the laser beam is performed selectively and development is further performed, so that the mask is formed in the area irradiated with the laser beam. Subsequently, the conductive film can be formed in a desired pattern by etching the conductive film using this mask. Accordingly, the circuit pattern of a TFT (a thin film transistor) or an IC can be made.
A method to divide a laser beam into a plurality of beam spots using a digital micromirror device (DMD) is known to form a desired irradiation pattern by a laser direct imaging method. The DMD is a device in which a plurality of minute micromirrors are aligned two-dimensionally, and because each of a plurality of micromirrors operates individually, desired irradiation patterns can be created on an irradiated surface. In addition, since the response time of the plurality of micromirrors constituting the DMD is extremely short such as several μs, plural patterns can be changed at high speed. A laser light-exposure apparatus using a DMD is suggested in view of such advantages (for example, patent document 1).
A DMD is a reflection type optical modulation element in which a plurality of minute micromirrors are aligned two-dimensionally. The DMD includes a micromirror, a hinge to fix the micromirror, a yoke, a CMOS memory semiconductor, and the like, and controls the tilt of each micromirror by generating an electrostatic force under the micromirror. The micromirror can be manufactured with a size of about several tens of μm, and each micromirror's angle becomes about ±10% variable responding to signals “1” and “0” which are added to an address electrode.
When the laser irradiation is performed using the DMD, the beam spot which is formed by each micromirror is required to have an equal beam characteristic to each other. In particular, in a light-exposure process of a semiconductor film and the like, microfabrication in a size of several μm is required. Therefore, in order to perform such microfabrication precisely, the spot size, energy, and the like of the beam spot are required to be homogenized at high level. Thus, when the laser beam is incident on the DMD and forms the irradiation pattern, an energy distribution of the laser beam is homogenized beforehand. As the methods for homogenizing the laser beam, there are methods using a diffusion plate, a kaleidoscope, an array lens, and the like. [Patent Document 1] Japanese Patent Laid-Open No. 2005-275325 bulletin